merge_joins

# File activerecord/lib/active_record/relation/merger.rb, line 108
      def merge_joins
        return if other.joins_values.blank?

        if other.klass == relation.klass
          relation.joins!(*other.joins_values)
        else
          joins_dependency, rest = other.joins_values.partition do |join|
            case join
            when Hash, Symbol, Array
              true
            else
              false
            end
          end

          join_dependency = ActiveRecord::Associations::JoinDependency.new(other.klass,
                                                                           joins_dependency,
                                                                           [])
          relation.joins! rest

          @relation = relation.joins join_dependency
        end
      end